This paper presents results of comprehensive analysis of BP horizontal well productivity and completion performance data. The study was performed to benchmark performance of existing horizontal wells with a view of developing simple empirical techniques that could be used for predicting performance of future wells. The developed correlation predicts a range of expected well productivity for future wells. This prediction reflects limitations of current completion technology and possible reservoir heterogeneities. The analysis method is based on presenting the existing well productivity data in the form of dimensionless parameters: the well productivity coefficient and the normalized productivity improvement factor. The results of this study can be used to:
sense check estimate of theoretical well performance for undeveloped discoveries with historical performance for similar type reservoirs
provide quality control for newly commissioned wells to see if performance is as expected
help optimize development well design (i.e. high angle vs. conventional) to optimize reservoir exploitation
offer a means to rank well surveillance work based on where initial well performance lay with respect to global historic experience.
Now a well established technology, the application of horizontal wells has added significant value to oil and gas field development in terms of increased recovery/reserves access and improved well rates that they can offer. Their applications are well-understood - notable examples being the improved drainage of naturally fractured reservoirs, better recovery from oil rims in gas fields and the production of heavy oil.
While their application on conceptual level is well understood, the performance actually delivered by this well type is not as clear. This leads to uncertainties as to the suitability of this well type for individual reservoir development. Similarly, while numerous theoretical analytical and numerical models exist to predict performance, there is an absence of an empirically based correlation, derived from actual field data. If such a technique were available, it would help to better understand a lot of the uncertainties that govern horizontal well performance - both in terms of predictive capability, along with benchmarking actual field results with the historic track record.
Works published in 19951,2 started to address this issue. Using well rates as the measure of success, these papers demonstrated the huge rate gains to be obtained in comparison to vertical offsets. This analysis was supported by an impressively large data set - 230 fields yielding information on 1,306 wells. Fields were broadly categorized into "conventional", "heavy oil" and "fractured". In this analysis, the fractured reservoir category indicated the largest rate gains (up to 12 fold increase) while the conventional category yielded a more modest 4-fold increase.
Around the same time, with an ever increasing usage of horizontal wells, BP identified the need to better understand how successfully horizontal wells were being applied around the world. While considerable work was being performed at an individual field level looking at horizontal well targeting and performance, no generic metrics existed to benchmark performance between different fields. As a consequence, a study was initiated to perform cross field/basin comparison and focusing only on initial well productivity. In this study, no attempt was made to address the issues of recovery, sweep efficiency etc. The results of the study were documented in an internal BP report3 and have been widely used within the company. Recently, this initial work was extended to include more wells. The results of this study are presented in this paper.